PROJECT SUMMARY AND ABSTRACT Caspase-1 is a cysteine protease that catalyzes the maturation of cytokines and plays critical roles in the innate and adaptive immune response to pathogenic stimuli. Misregulation of caspase-1 is associated with various autoimmune diseases and cancer. Similarly, caspase-2 is a cysteine protease that is important for regulating the cellular response to stresses that cause DNA damage, such as chemotherapy. Both caspase-1 and caspase- 2 are activated by structurally similar sensor proteins that sense intracellular perturbations and mount appropriate responses, but the molecular mechanism of how the sensors are activated and then in turn activate their respective proteases, is not well understood. A series of germline-encoded pattern recognition receptors sense conserved features of pathogens, and assemble into multiprotein complexes called inflammasomes, which recruit and activate caspase-1. The consensus model for caspase-1 activation is that inflammasomes are first activated then they in turn activate caspase-1. Our preliminary data suggests that caspase-1 plays a role in inflammasome activation, which in turn activates more caspase-1, however, the molecular mechanism is unknown. The goal during the K99 mentored phase, is to determine the role caspase-1 plays in inflammasome activation. Specifically, we will determine the activation mechanism of the ZU5 domain-containing inflammasomes, CARD8 and NLRP1. During the independent R00 phase, we will then apply the training from the mentored phase to determine the activation mechanism of another ZU5 domain-containing sensor that activates caspase-2 in response to genotoxic stress, PIDD. Our central hypothesis is that the ZU5 domain- containing sensor proteins are activated in a similar manner, in which the proteases they activate participate in sensor activation, which in turn activates more protease. To accomplish these goals, I have carefully assembled a highly complementary advisory team with the scientific and mentoring skills needed to guide my path to research independence. The completion of this work will further our understanding of pyroptosis and apoptosis regulation and could potentially advance therapeutic development efforts for a variety of human diseases.